The invention relates to an activated carbon filter, particularly for reducing the vapor emissions from a fuel system of a vehicle, including a first and a second connecting section, a filter section including activated carbon between the two connecting sections and a filter layer which consists of a highly effective adsorber material and which has an activated carbon section disposed adjacent to, and covering, the first connecting section.
An activated carbon filter of the type referred to above is known from DE 197 08 692 A1. It discloses an adsorption filter with a first and a second filter area. The first filter area includes a coarse filter. It is filled with activated carbon or another adsorber material and has a high adsorption capacity and a low pressure loss. The second filter area consists of a textile activated carbon surface structure based on a fleece or a fabric and is used to enclose or cover the coarse filter.
In order to prevent in motor vehicles the release of hydrocarbon-containing fuel vapors from a fuel tank or a carburetor of a motor vehicle, fuel supply system are sealed structures and include activated carbon filters. When the internal combustion engine is at a standstill, fuel vapors escaping from the tank area of the fuel supply system reach the activated carbon filter where most of the hydrocarbon components are retained and prevented from escaping into the environment. When the internal combustion engine is operating, the activated carbon filter is flushed with intake air. In this process, the hydrocarbons deposited in the filter are again supplied to the internal combustion engine for combustion therein.
DE 36 09 976 C2 discloses an activated carbon filter for a fuel supply system of a motor vehicle which includes a container filled with activated carbon particles. This container includes at one side an opening for the admission of fresh air which opening is covered by filter material. At the opposite side of the container, means are provided for the connection of he activated carbon filter to the fuel supply system. In the area of the opening for the admission of fresh air to the activated carbon filter, an electric heating arrangement is provided in the form of a metallic grid structure. When the engine is slut down, hydrocarbon-containing gas evaporates from the fuel supply system and reaches the activated carbon filter, which adsorbs the hydrocarbons. As the engine is started, fresh air flows into the activated carbon filter through the respective opening. The fresh air is preheated by the heating arrangement, whereby the activated carbon filter is regenerated as soon as engine operation begins and the hydrocarbons adsorbed by the activated carbon particles are released and supplied to the internal combustion engine for combustion therein.
DE 25 00 470 A1 discloses a filter element which includes fibers of activated carbon. The fibers of activated carbon are in the form of a woven fabric or a fleece and several layers thereof are disposed in the filter housing so as to extend in a plane normal to the flow direction of a gas to be filtered. For the separation of the layer of activated carbon, spacer elements are provided, which consist of a thermoplastic polymer.
It is further known from DE 195 14 887 A1 to provide in air cleaning systems a thin filter layer consisting of an adsorbing cover fleece which may contain activated carbon.
It is the object of the present invention to provide an activated carbon filter of the type referred to above with which hydrocarbons can be practically fully filtered out of a gas mixture with a high hydrocarbon content so that their escape into the environment is prevented and the filter can be again effectively desorbed in a simple and effective manner.
In an activated carbon filter for reducing vapor emissions from a fuel supply system including, in a filter housing, a first connecting section for communication with the atmosphere and a second connecting section for communication with the fuel supply system, an activated carbon filter section is disposed between the first and second connecting sections and a filter layer of a highly adsorptive filler material layer is disposed between the activated carbon filter section and the first connecting section to prevent any escape of vapors through the first connecting section to the atmosphere.
With this activated carbon filter, the hydrocarbon emissions from a fuel system can be reduced to almost zero. This is also true when the filter is heated since the released hydrocarbons are prevented from escaping through the fresh air inlet by the highly adsorptive filter layer.
If the filter layer consists of an electrically conductive adsorber material and can be electrically heated, the filter serves at the same time as the electric heating arrangement. It provides in a simple manner for a rapid regeneration of the activated carbon filter.
The filter layer may also consist of a highly adsorptive material including an activated carbon fabric or an activated carbon fiber fleece. Such a structure provides for a filter layer with a particularly high adsorption capability.
In an advantageous embodiment of the invention, the filter section with activated carbon comprises a housing with at least a first and a second chamber. The chambers are filled with activated carbon pellets. The connecting section for the fuel system is disposed adjacent the first chamber and the connecting section for the fresh air supply is disposed adjacent the second chamber. The two chambers are in communication with each other at the ends thereof remote from the fuel system and gas supply connections by way of a filter fleece or filter fabric. In this way, the activated carbon filter provides for the gas to be filtered a long travel path while the filter arrangement is still relatively small.
It is advantageous if the filter fleece/fabric, which is arranged between the first and the second chambers is provided with a spring-loaded pressure plate which biases the filter fleece/fabric against the activated carbon pellets in the first and, respectively, second chambers. In this way, the activated carbon pellet volume remains compact and dense.
Also, the connecting section for the fuel supply system includes a connector for connection with the fuel tank and a connector for connection with a suction arrangement of the internal combustion engine. A filter fleece/fabric is disposed between the filter section, which includes activated carbon, and the connector for the suction arrangement. The connection for the fuel tank includes preferably a tubular housing structure of a net-like filter fabric, which extends into the activated carbon filter section. In this way, it is made sure that fuel vapors from the fuel supply system are adsorbed in the activated carbon filter over the largest possible activated carbon surface area.
Further features and advantages of the invention will become apparent from following description thereof on the basis of the accompanying drawing.